Graphene, a single atomic layer of carbon, is known in the art. Sometimes even several layers of graphene may be referred to in the art as graphene. Two-dimensional (2D) structured carbon sheets of graphene can provide the basic building blocks for carbon allotropes of graphite (a three-dimensional (3D) material), nanotubes (a one-dimensional (1D) material), and fullerenes (a zero-dimensional (0D) material). Graphene is predicted to have exceptional properties such as large thermal conductivity, superior mechanical properties, and excellent electronic transport properties. Although not wanting to be bound by theory, it is believed that electrons in graphene follow a linear dispersion relationship, and behave like mass-less relativistic particles.
Currently, production or growth of graphene films evolves around mechanical exfoliation (e.g., obtaining graphene by physically peeling off the surface layers of graphite using adhesive (e.g., transparent) tape (such as that available under the trade designation “MAGIC TAPE” from 3M Company, St. Paul, Minn.)), chemical exfoliation, and epitaxial growth methods (e.g., chemical vapor deposition (CVD) and plasma enhanced chemical vapor deposition). These techniques require a liquid, adhesive or gaseous vapor inside a high temperature apparatus to deposit the graphene or graphitic thin films onto substrates. Further, these techniques are not able to produce and process graphene with good repeatability.
Further, these methods of providing graphene also leave contaminates deposited at the molecular level. For example, depositing thin molecular layers via Langmuir-Blodgett (LB), layer-by-layer (LBL) deposition uses liquids which contaminate the deposit at the molecular level. Energy intensive methods such as chemical vapour deposition (CVD) and molecular beam epitaxy (MBE) utilize another substrate to deposit a layer of the material of interested which is subsequently transferred to a substrate of interest. In doing so, apart from the complication of the work flow, extraneous materials (e.g., catalyst and, substrate molecules) are incorporated into the deposit. These residual contaminants have to be cleaned by an additional step to obtain pristine deposits.
Most often Applicants have seen the adhesive tape approach referred to in the published work on graphene. The yield of the exfoliated graphene with this technique is relatively low, typically one 100 squared micrometer flake over a 100 mm2 substrate. Adding to the challenge, un-exfoliated graphite on the substrate tends to hinder the fabrication/patterning of metal contacts by short circuiting the device. Thus far, the most feasible way to study graphene is by using e-beam writer for device fabrication. Even though e-beam writing allows novel patterns and circuitry to be fabricated, the technique is tedious and different layout designs are needed for each substrate. This is currently a bottleneck of bringing graphene research to the mainstream materials science community.
Furthermore, it is still a challenge to selectively place the graphene as desired, which is important, for example, in device fabrication and system integration. Further, graphene and its electrical performance is very sensitive to substrate surfaces and the environment, including contaminants. Alternative, more useful forms (e.g., sizes) of graphene and methods for providing those forms and placing them on surfaces is desired.